Safety chain locks of the kind commonly employed on the doors of homes and apartments are relatively ineffective for the simple reason that the usual chain end anchor elements are held very insecurely by a pair of retainers on the interior side of the door and on the corresponding side of the adjacent door frame. These retainers are usually fastened to the door and door frame by two or more wood screws, with the result that a shoulder of an intruder placed firmly against the door can easily rip one or both of the screw anchored retainer elements from the door or frame. Only in cases where metal doors and door frames are employed can these customary prior art structures have even minimal security.
Consequently, there is a distinct need in the art for improved safety chain locks for doors, and it is the object of this invention to completely satisfy this need in a practical and economic way by providing an improved and much more secure mounting means for chain end anchors, whereby the lock can readily withstand the forces of an intruder even when installed on a wooden door and door frame. More particularly, one chain end anchor is secured to the interior face of the door frame by an L-shaped or angle retainer which embraces the interior corner of the frame in two right angular planes. The web of this retainer which receives the adjacent door lock bolt is serrated and tightly clamped to the frame by an overlying serrated clamp plate which also receives the door lock bolt.
The opposite chain end anchor is removably engaged in a heavy slotted retainer plate which is similarly clamped to the edge of the door through which the lock bolt projects. An interior extension of the retainer plate is engaged over the interior portion of the door lock housing assembly which is immovable and unseparable from the outer assembly portion except when the door is open to expose the dead bolt. In this manner, the retainer plate for the adjustable or separable chain end anchor is doubly reinforced at its ends and very firmly secured to the door lock housing assembly. As a consequence, it is virtually impossible to dislodge the chain anchor retainers from their moorings on the door frame and door.
The invention while illustrated in association with a certain preferred form of door lock mechanism is equally adaptable to a variety of doors and door lock mechanisms.
Other features and advantages of the invention will become apparent during the course of the following description.